/*******************************************
libudev example.
This example prints out properties of
each of the hidraw devices. It then
creates a monitor which will report when
hidraw devices are connected or removed
from the system.
This code is meant to be a teaching
resource. It can be used for anyone for
any reason, including embedding into
a commercial product.
The document describing this file, and
updated versions can be found at:
http://www.signal11.us/oss/udev/
Alan Ott
Signal 11 Software
2010-05-22 - Initial Revision
2010-05-27 - Monitoring initializaion
moved to before enumeration.
*******************************************/
#include
#include
#include
#include
#include
int main (void)
{
struct udev *udev;
struct udev_enumerate *enumerate;
struct udev_list_entry *devices, *dev_list_entry;
struct udev_device *dev;
struct udev_monitor *mon;
int fd;
/* Create the udev object */
udev = udev_new();
if (!udev) {
printf("Can't create udev\n");
exit(1);
}
/* This section sets up a monitor which will report events when
devices attached to the system change. Events include "add",
"remove", "change", "online", and "offline".
This section sets up and starts the monitoring. Events are
polled for (and delivered) later in the file.
It is important that the monitor be set up before the call to
udev_enumerate_scan_devices() so that events (and devices) are
not missed. For example, if enumeration happened first, there
would be no event generated for a device which was attached after
enumeration but before monitoring began.
Note that a filter is added so that we only get events for
"hidraw" devices. */
/* Set up a monitor to monitor hidraw devices */
mon = udev_monitor_new_from_netlink(udev, "udev");
udev_monitor_filter_add_match_subsystem_devtype(mon, "hidraw", NULL);
udev_monitor_enable_receiving(mon);
/* Get the file descriptor (fd) for the monitor.
This fd will get passed to select() */
fd = udev_monitor_get_fd(mon);
/* Create a list of the devices in the 'hidraw' subsystem. */
enumerate = udev_enumerate_new(udev);
udev_enumerate_add_match_subsystem(enumerate, "hidraw");
udev_enumerate_scan_devices(enumerate);
devices = udev_enumerate_get_list_entry(enumerate);
/* For each item enumerated, print out its information.
udev_list_entry_foreach is a macro which expands to
a loop. The loop will be executed for each member in
devices, setting dev_list_entry to a list entry
which contains the device's path in /sys. */
udev_list_entry_foreach(dev_list_entry, devices) {
const char *path;
/* Get the filename of the /sys entry for the device
and create a udev_device object (dev) representing it */
path = udev_list_entry_get_name(dev_list_entry);
dev = udev_device_new_from_syspath(udev, path);
/* usb_device_get_devnode() returns the path to the device node
itself in /dev. */
printf("Device Node Path: %s\n", udev_device_get_devnode(dev));
/* The device pointed to by dev contains information about
the hidraw device. In order to get information about the
USB device, get the parent device with the
subsystem/devtype pair of "usb"/"usb_device". This will
be several levels up the tree, but the function will find
it.*/
dev = udev_device_get_parent_with_subsystem_devtype(
dev,
"usb",
"usb_device");
if (!dev) {
printf("Unable to find parent usb device.");
exit(1);
}
/* From here, we can call get_sysattr_value() for each file
in the device's /sys entry. The strings passed into these
functions (idProduct, idVendor, serial, etc.) correspond
directly to the files in the /sys directory which
represents the USB device. Note that USB strings are
Unicode, UCS2 encoded, but the strings returned from
udev_device_get_sysattr_value() are UTF-8 encoded. */
printf(" VID/PID: %s %s\n",
udev_device_get_sysattr_value(dev,"idVendor"),
udev_device_get_sysattr_value(dev, "idProduct"));
printf(" %s\n %s\n",
udev_device_get_sysattr_value(dev,"manufacturer"),
udev_device_get_sysattr_value(dev,"product"));
printf(" serial: %s\n",
udev_device_get_sysattr_value(dev, "serial"));
udev_device_unref(dev);
}
/* Free the enumerator object */
udev_enumerate_unref(enumerate);
/* Begin polling for udev events. Events occur when devices
attached to the system are added, removed, or change state.
udev_monitor_receive_device() will return a device
object representing the device which changed and what type of
change occured.
The select() system call is used to ensure that the call to
udev_monitor_receive_device() will not block.
The monitor was set up earler in this file, and monitoring is
already underway.
This section will run continuously, calling usleep() at the end
of each pass. This is to demonstrate how to use a udev_monitor
in a non-blocking way. */
while (1) {
/* Set up the call to select(). In this case, select() will
only operate on a single file descriptor, the one
associated with our udev_monitor. Note that the timeval
object is set to 0, which will cause select() to not
block. */
fd_set fds;
struct timeval tv;
int ret;
FD_ZERO(&fds);
FD_SET(fd, &fds);
tv.tv_sec = 0;
tv.tv_usec = 0;
ret = select(fd+1, &fds, NULL, NULL, &tv);
/* Check if our file descriptor has received data. */
if (ret > 0 && FD_ISSET(fd, &fds)) {
printf("\nselect() says there should be data\n");
/* Make the call to receive the device.
select() ensured that this will not block. */
dev = udev_monitor_receive_device(mon);
if (dev) {
printf("Got Device\n");
printf(" Node: %s\n", udev_device_get_devnode(dev));
printf(" Subsystem: %s\n", udev_device_get_subsystem(dev));
printf(" Devtype: %s\n", udev_device_get_devtype(dev));
printf(" Action: %s\n", udev_device_get_action(dev));
udev_device_unref(dev);
}
else {
printf("No Device from receive_device(). An error occured.\n");
}
}
usleep(250*1000);
printf(".");
fflush(stdout);
}
udev_unref(udev);
return 0;
}